This invention relates to a magnetic tape cassette comprising reels on which a magnetic tape is wound, and a reel lock member which is engageable with the teeth of the reels.
Magnetic tape cassettes are popularly employed as recording media. FIG. 7 is an exploded perspective view of a DVC (digital video cassette), namely, a magnetic tape cassette 20.
As shown in FIG. 7, the magnetic tape cassette 20 comprises a cassette body, a magnetic tape (not shown) and an opening and closing lid 27. The cassette body comprises opening 21 an upper cassette half 22 and a lower cassette half 23. In front portion of the cassette body (left side in FIG. 7), the cassette body possesses opening 21 for inserting a tape pull-out member equipped in a video tape recorder (VTR). The magnetic tape (not shown) is laid tight in the opening 21 with the aid of tape guides 37 and 38 which are provided on the front surface of the cassette body. The opening and closing lid 27 is provided on the front of the cassette body, and comprises an outer lid (or front lid) 29, a top lid (or upper lid) 30 and an inner lid (or rear lid) 31.
In the lower cassette half 23, a pair of reels 35 and 36 are rotatably provided and a magnetic tape is wound on the reels 35 and 36. The reels 35 and 36 comprise disk-shaped upper flanges 39 and 40 and disk-shaped lower flanges 41 and 42. The disk-shaped lower flanges 41 and 42 are integrally molded with cylindrical hubs 41a and 42a, and have engaging teeth 43 and 44 along the whole peripheries thereof, respectively.
When the magnetic tape cassette 20 is not loaded in a device such as a VTR, i.e., when the cassette is stored or carried, the magnetic tape has the possibility to be slackened. In order to prevent the magnetic tape from being slackened, a reel lock member 45 and a lock spring 46 are provided. The reel lock portion 45 is provided in the space formed on the rear side of the cassette and between the reels 35 and 36, and functions to prevent the rotation of the reels 35 and 36. The lock spring 46 is provided and adapted to urge the reel lock member 45.
On the other hand, recently there has been a strong demand for an increase in recording capacity. However, the outer dimensions of the cassette body cannot be increased so much because of the dimensional limits of the hardware side. Therefore, the following method has been employed: the hub diameter of the reels, on which the magnetic tape is wound, is decreased in diameter, and the flange diameter of the reels is increased, while the reel accommodating area of the cassette half which is adapted to accommodate the reels is increased. For instance, as shown in FIG. 8, the reel accommodating areas 50 of the lower half 23 are made larger than those of the prior art according to the large diameter reels 35a of which flange diameter d1 is larger.
FIG. 9 is an exploded diagram of the lower half 23a which accommodates reels 35b having an ordinary flange diameter d2, showing only the left reel for simplification in description. As shown in FIG. 9, in order to stop the rotation of the reel 35b, the engaging pawls 45a of the reel lock member 45 are engaged with the engaging teeth 43b of the reels 35b. However, since the reel accommodating area 50 is formed according to the large diameter reel 35a the flange of which is large in diameter, as shown in FIG. 10, when the cassette is dropped or vibrated the reel 35b having the ordinary flange diameter may be shifted to the front and to the side, or leave a track. Then, as shown in FIG. 11, when it is intended to stop the rotation of the reel, the engaging pawl 45a of the reel lock member 45 cannot engage with the engaging teeth 43b of the reel 35b. 
In view of the foregoing, an object of the invention is to provide a magnetic tape cassette in which, regardless of the outside diameter of the reels accommodated therein, the rotation of the reels can be positively stopped.
The above-mentioned object can be achieved by a magnetic tape cassette comprising:
a reel on which a magnetic tape is wound and which turns on a predetermined track and has an engaging teeth at its periphery;
a cassette half having a reel accommodating area which is accommodatable various kind of reels which are different in an outside diameter from one another;
a reel lock member disposed on the cassette half and having an engagement pawl, the reel lock member being slidable between a reel lock position where the engagement pawl of the reel lock member is engaged with the engaging teeth of the reel so as to inhibit a rotation of the reel and a releasing position where the reel lock member disengages from the engaging teeth of the reels so as to allow the rotation of the reel; and
a rib disposed on the cassette half for keeping a locking condition where the engagement pawl is engaged with the engaging teeth, when the reel leaves from the predetermined tracks.
In the above construction of the magnetic tape cassette according to present invention, it is preferable that the rib is substantially confronted with a tip end of the engagement pawl about a center of the reel.
In the above construction of the magnetic tape cassette according to the present invention, it is preferable that the shortest distance defined between the rib and the tip end of the engagement pawl of the reel locking member, which is located in the reel lock position, is shorter than the outside diameter of the reel.
In the above construction of the magnetic tape cassette according to present invention, it is preferable that the engagement pawl is extended in a line, and the rib is substantially disposed on the line.
Further, in the above construction of the magnetic tape cassette according to present invention, it is preferable that the cassette half is formed by injection molding with a main metal mold, and the rib is formed by injection molding with an insert mold which is attachable to the main metal mold.
The above-mentioned object can be also achieved by a metal mold, according to a present invention, used for manufacturing a magnetic tape cassette including,
a reel on which a magnetic tape is wound and which turns on a predetermined track and has a engaging teeth at its periphery,
a cassette half having a reel accommodating area which is accommodatable various kind of reels which are different in its outside diameter,
a reel lock member disposed on the cassette half and having an engagement pawl, the reel lock member being slidable between a reel lock position where the engagement pawl of the reel lock member is engaged with the engaging teeth of the reel so as to inhibit a rotation of the reel and a releasing position where the reel lock member disengages from the engaging teeth of the reels so as to allow the rotation of the reel, and a rib disposed on the cassette half for keeping a locking condition where the engagement pawl is engaged with the engaging teeth, when the reels leave from the predetermined tracks,
the metal mold comprising:
a main metal mold portion forming the cassette half by an injection molding; and
an insert metal mold portion being attachable to the main metal mold portion for forming the rib by the injection molding simultaneously.
According to the invention, even with a cassette half having a reel accommodating area in correspondence to maximum diameter reels, when the reel accommodated therein leaves the track, the rib provided in the reel accommodating area regulates the position of the reel to the reel lock position, so that the reel lock member stops the rotation of the reel. Accordingly, even when the cassette for instance drops to cause the reel leave the track, the rotation of the reel can be positively stopped, and accordingly the magnetic tape will never be slackened.
Furthermore, in the magnetic tape cassette, a part of a metal mold adapted to form the cassette half by injection-molding which is to form the rib is an insert metal mold portion, and the rib is formed by injection molding with the insert metal mold portion set in the metal mold.
In the use of the metal mold, the rib of the cassette half is formed by injection molding with the insert metal mold inserted therein. Accordingly, it is unnecessary to set a stationary metal mold and a movable metal mold in a molding machine separately according to whether or not the lower half has the position regulating rib. Owing to this feature, the magnetic tape cassette can be manufactured with high efficiency and at low cost.